Microfibrous entrapped catalysts (MFECs) have been developed for strong exothermic or endothermic processes. The sintered metal microfibrous structure can collect the heat from the catalyst particles, where the reaction heat is generated and transfer it to the internal reactor wall-MFEC contacting interface. MFECs made of copper microfibers demonstrate 50-200 times enhancement in effective thermal conductivity compared with typical packed catalyst beds (Sheng and Yang, 2012). Because MFECs are flexible, the can be deformed to match any solid surface geometry. The heat transfer at the wall-MFEC interface is comparable to the heat transfer of a phase change (e.g. water evaporation), which is a very fast heat transfer approach.
Because of these fast heat transfer characteristics, MFECs can provide uniform temperature profiles and enable fine temperature control for strong exothermic and endothermic reaction/processes even at fast reaction rates. This is critical to temperature sensitive reactions or processes, especially reactions or processes that are strongly exothermic or endothermic, for example Fischer Tropsch synthesis, methanol synthesis, ethyl oxide formation, and the like.
According to a heat transfer resistance analysis of a MFEC-wall system (FIG. 1), the heat transfer resistance on the wall-MFEC interface accounts for 75% of overall heat transfer resistance in the system. This result suggests that the wall MFEC-contacting interface becomes the limiting step for heat transfer. In order to further improve heat transfer, the interfacial heat transfer must be improved.
Therefore, it is an object of the invention to provide methods for improving heat transfer at the wall-MFEC interface.
The principle of heat transfer can be described in terms of effective thermal conductivity by equation 1,
                    Q        =                  k          ⁢                                          ⁢                      A            l                    ⁢          Δ          ⁢                                          ⁢          T                                    Equation        ⁢                                  ⁢        1            where Q is heat transfer rate, k is the effective thermal conductivity, A is the heat transfer area, and l the heat transfer distance, and ΔT is the temperature gradient at wall. In most cases, l is a constant determined by the size of reactor and a low ΔT and a high Q are desired simultaneously. In these cases, faster heat transfer rate (Q) can be achieved commonly by improving the effective thermal conductivity (k) at the internal wall and increasing heat transfer area (A).
Increasing heat transfer area (A) is a common approach used to improve the heat transfer from gas stream passing through the heat exchanging tube. It will certainly benefit the microfibrous media, microfibrous entrapped catalysts (MFEC) or microfibrous entrapped sorbents (MFES). Due to the unique characteristics of microfibrous media, such as flexibility and deformability, increase in heat transfer area (A) will bring more benefits. Moreover, specific approaches can be taken to improve the k of the heat transfer process.